I have written quite a few times about the lake. I will however, provide some information that I have given before again, for people who don't necessarily want to go to the links I will provide later in this post.
Lake Vouliagmeni (Sunken Lake) is a small brackish-water lake fed by underground currents seeping through the mass of Mount Hymettus but it is also supplied with warm seawater (28-35oC) via an underground channel spreading through a network of flooded caves. Consequently, the water temperature never drops below 18oC (usually ranges around 22-25oC). Furthermore, a freshwater spring reduces its salinity. These are quite unique environmental conditions.
The lagoon formed about 2,000 years ago. It was once a large cavern that collapsed following an earthquake. The outline of the cavern roof can be clearly seen from a distance as you can see from this photograph that was taken from across the bay.
The lake continues deep inside the mountain in an underwater cave never fully explored, as its end seems impossible to trace even by employing sonar detection. Many underwater expeditions have been carried out in order to chart it, a number amateur divers have drowned while trying to explore, as have three professional ones.
Because of its constant warm water temperature and its rich content of various minerals, the lake functions as a spa since the end of the 19th century. It also hosts the only existing population of species of sea anemone, Paranemonia Vouliagmeniensis.
A cave. I used to love swimming towards and under it, but they have cordoned it off now - they are constantly worried about people injuring themselves or worse
and here it is, a few people swimming
We did want to sit in the sun, but that would have meant no views of the lake
so we sat in the shaded area
On the edge there is a sign that gives you daily information about the lake. When I took this photograph the time was 13:42, the temperature was 16oC and the water temperature was 22oC.
While we ate I was watching this woman who looked to be in her middle 80s doing some exercises after her swim. And then she did this. Wow! Such level of fitness. Amazing.
I would finally like to share three links. The first one which you can see here was written while I was reading A Lacuna by Barbara Kingsolver and I realised that the lake is a lacuna. In the post I juxtapose my impressions of the lake with quotes from this wonderful novel. This post also provides the best and most comprehensive pictures of the lake.
The second link which you can see here is about an evening we spent at the lake.
The third link, here , is about a play we saw that was performed in a smaller lake, just behind this one, a truly enchanted evening.